the only way they could check if there was a current connection would be if they wrote a function into the script that checked for recent activity every so often
downsides to that would include it being highly innaccurate depending on how often it checked and if it checked too often it would slow down the server considerably depending on the load. it could adjust the frequency of checking dynamically i guess but i doubt they went through that much trouble for something so unnecessary.
even if it got checked every hour, there would probably be an abundance of names to update, also significantly delaying the response time of the server (for perhaps a short amount of time). not to mention that users would appear as ghosts. seen but unable to be contacted.